Polishing device and polishing method

ABSTRACT

In one embodiment, a polishing device includes: a rotatable turntable, a holding unit, a separation wall, a slurry supply tube, and a cooling medium supply tube. On an upper surface of the rotatable turntable, a polishing pad is attached. The holding unit rotatably holds an object to be polished and disposes a polished surface of the object to be polished in a manner to face the polishing pad. The separation wall abuts on the upper surface of the polishing pad and sections the polishing pad into a polished region in which the holding unit is provided and an unpolished region in which the holding unit is not provided. The slurry supply tube supplies a slurry to the upper surface of the polishing pad in a polished region side. The cooling medium supply tube supplies a cooling medium to the upper surface of the polishing pad in the unpolished region.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-231447, filed on Oct. 5, 2009; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a polishing device and a polishing method used for a CMP (Chemical Mechanical Polishing) method.

BACKGROUND

Recently, in a manufacturing field of a semiconductor device, as semiconductor devices become highly densified and miniaturized, various microfabrication technologies are used. Among those technologies, a chemical mechanical polishing (CMP) technology is essential for planarization of an interlayer insulation film, formation of a plug, formation of a buried metal wiring, buried metal isolation or the like.

In a polishing device for CMP, a turntable on whose upper surface a polishing pad is attached is rotated in a horizontal plane, and a slurry is supplied by a slurry supply tube from above the polishing pad. The slurry wets an entire surface of the polishing pad and a slurry layer is formed on the polishing pad. While a top ring holding a semiconductor wafer is rotated in the horizontal plane in the same direction as rotation of the turntable, the top ring presses this polishing pad. A surface to be polished of the semiconductor wafer is polished by being rubbed against the polishing pad via the slurry.

Due to heat generation by such rubbing (friction), a temperature of the surface of the polishing pad rises. The temperature rise is made larger by the following conditions (1) to (4). (1) Pressing force of the semiconductor wafer to the polishing pad is large. (2) A rotation speed of the top ring or the turntable is large. (3) A flow amount of the slurry is small. (4) An area of the semiconductor wafer is large.

Thus, the surface temperature of the polishing pad may sometimes exceed several ten degrees, 50° C. for example. As a result, the surface of the polishing pad is softened, and there is a possibility that a planarization characteristic of the semiconductor wafer in a CMP process is deteriorated. The semiconductor wafer has a tendency to have a larger diameter as the generation advances. Further, in view of cost reduction, there is a tendency that a flow amount of a slurry per semiconductor wafer unit area is reduced. Therefore, there is a possibility that the temperature rise of the polishing pad becomes larger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front view schematically showing a polishing device according to a first embodiment and showing a part thereof by a cross section (hatching portion).

FIG. 1B is a top view schematically showing the polishing device according to the first embodiment and showing a part thereof by a cross section (hatching portion).

FIG. 1C is a view schematically showing the polishing device according to the first embodiment and is a cross-sectional view of a separation wall along a line X-Y in FIG. 1B.

FIG. 1D is a view schematically showing the polishing device according to a variation of the first embodiment and is a cross-sectional view of a separation wall along a line X-Y in FIG. 1B.

FIG. 2 is a graph showing a temperature distribution of a polishing pad of the polishing device according to the first embodiment.

FIG. 3 is a top view schematically showing a polishing device according to a second embodiment and showing a part thereof by a cross section (hatching portion).

FIG. 4A is a front view schematically showing a polishing device according to a third embodiment and showing a part thereof by a cross section (hatching portion).

FIG. 4B is a top view schematically showing the polishing device according to the third embodiment and showing a part thereof by a cross section (hatching portion).

FIG. 5 is a graph showing a temperature distribution of a polishing pad of the polishing device according to the third embodiment.

DETAILED DESCRIPTION

In one embodiment, a polishing device includes a rotatable turntable, a holding unit, a separation wall, a slurry supply tube, and a cooling medium supply tube. On an upper surface of the rotatable turntable, a polishing pad is attached. The holding unit rotatably holds an object to be polished and disposes a polished surface of the object to be polished in a manner to face the polishing pad. The separation wall abuts on the upper surface of the polishing pad and sections the polishing pad into a polished region in which the holding unit is provided and an unpolished region in which the holding unit is not provided. The slurry supply tube supplies a slurry to the upper surface of the polishing pad in a polished region. The cooling medium supply tube supplies a cooling medium to the upper surface of the polishing pad in the unpolished region.

Hereinafter, embodiments will be described with reference to the drawings. In the following drawings, the same reference numeral is given to the same component.

First Embodiment

A polishing device and a polishing method according to a first embodiment will be described with reference to FIG. 1A and FIG. 1B.

As shown in FIG. 1A and FIG. 1B, a polishing device 1 has, schematically, a turntable 11, a separation wall 21, a top ring 25, a slurry supply tube 31, and a cooling medium supply tube 35. The turntable 11 is housed in a casing 15 in which a funnel 16 is provided along an outer periphery of the turntable 11. The separation wall 21 sections a polishing pad 12 on the turntable 11. The top ring 25 is a holding unit to hold a semiconductor wafer 27 being an object to be polished.

The turntable 11 has a radius in which the top ring 25 holding the semiconductor wafer 27 can be placed. The polishing pad 12 is attached on an upper surface of the turntable 11. The polishing pad 12 is formed of polyurethane foam for example, and more specifically, of IC1000/SUBA400 of Rodel Nitta Co., Ltd. and so on. The polishing pad 12 of the turntable 11 is rotated in a horizontal plane. A rotation direction is clockwise as shown in FIG. 1B (shown by an arrow) for example.

Above the turn table 11 is disposed the top ring 25 suction-holding the semiconductor wafer 27 with a surface to be polished, a semiconductor device surface for example, facing to the polishing pad therebelow. The top ring 25 is rotated in the same direction (shown by an arrow) as that of the turntable 11 in horizontal plane. During the polishing, a surface to be polished of the semiconductor wafer 27 is pressed at a certain pressure so as to contact a surface of the polishing pad 12.

The top ring 25 has a retainer ring 29 disposed around the semiconductor wafer 27. An object of the retainer ring 29 is to prevent the semiconductor wafer 27 from deviating from the top ring 25 at a time of polishing and to prevent an edge portion of the semiconductor wafer 27 from being over-polished. However, it is possible not to use the retainer ring 29.

At the time of polishing, in a region (polish contact surface 37) excluding a center portion and a peripheral portion on the polishing pad 12, the polishing pad 12 and the top ring 25 holding the semiconductor wafer 27 contact each other. The polish contact surface 37 is an assemblage of trajectories on the polishing pad 12 made by the top ring 25 contacting the polishing pad 12. The polish contact surface 37 has a donut shape indicated by a broken line. It should be noted that a polish contact surface of the polishing pad 12 and the semiconductor wafer 27 is a region within the polish contact surface 37.

The separation wall 21 has a U shape (shape projecting toward a polished region 43 described later) in plain view for example. A bottom surface portion of the U shape of the separation wall 21 is disposed in the center portion of the polishing pad 12, that is, a position corresponding to a hole inside the polish contact surface 37 of a donut shape. The separation wall 21 is bent from the U-shaped bottom surface portion toward upper end portions, and the surface of the polishing pad 12 is sectioned in the U shape from a center to an outer periphery. The bent separation wall 21 contacts the outer periphery of the polishing pad 12 at two places in plain view. The separation wall 21 contacts the surface of the polishing pad 12 from right overhead. In other words, a side surface of the separation wall 21 is almost vertical to the polishing pad 12.

The separation wall 21 is bent in a crank shape in a direction of departing upward from the surface of the polishing pad 12 and further in a horizontal direction, outside the outer periphery of the polishing pad 12. The two places of the upper end portions of the U shape of the separation wall 21 are fixed to the casing 15. Fixing of the separation wall 21 to the casing 15 is done by a press jig 23 to which a spring is attached for example so that the separation wall 21 is able to be pressed constantly. It is preferable that a press load at which the separation wall 21 presses the polishing pad 12 is set to be equal to or lower than 9.8 kPa (100 gf/cm²). It is because friction heat between the separation wall 21 and the polishing pad 12 becomes large when the press load is made large.

Two places of the separation wall 21 contacting the outer periphery of the polishing pad 12 are apart from each other by about one fourth of the outer periphery for example along the outer periphery of the polishing pad 12. A portion surrounded by the separation wall 21 and about one fourth of the outer periphery of the polishing pad 12 is a region in which the top ring 25 is not provided, that is, an unpolished region 41. A portion (portion surrounded by the separation wall 21 and about three fourth of the outer periphery of the polishing pad 12) except the unpolished region 41 is a polished region 43. The top ring 25 is provided in the polished region 43.

The separation wall 21 can be divided into portions 21A and 21B at the center portion of the polishing pad 12. In a rotation direction upstream of the polishing pad 12 in the unpolished region 41, the portion 21A has a curve projecting toward the upstream. Further, in a rotation direction downstream of the polishing pad 12, the portion 21B has a curve projecting toward the downstream. It should be noted that the upstream means a side which the rotated polishing pad 12 first reaches within the unpolished region 41.

The top ring 25 is generally disposed in a center portion of the polished region 43 (that is, in a position, in the polished region 43, opposite to the unpolished region 41 in relation to the center of the polishing pad 12) along the rotation direction of the polishing pad 12. It should be noted that the top ring 25 and the unpolished region 41 are not required to be placed opposite to each other in relation to the center of the polishing pad 12. The top ring 25 can be disposed on one side of the part 21B of the separation wall 21. This makes a cooling efficiency higher because the cooled polishing pad 12 reaches directly under the top ring 25 within a short time.

As shown in FIG. 10, a cross section of the separation wall 21 is an almost rectangle with corners contacting the polishing pad 12 rounded. A height of the separation wall 21 is a height with which a later-described cooling medium does not flow over above the separation wall 21, about 2 cm for example. A width of the separation wall 21 is a width durable to a dynamic friction force from the rotated polishing pad 12. A material of the separation wall 21 is required to have a high chemical resistance and a high abrasion resistance. As the material, there can be used a material equivalent to that for the retainer ring 29 of the top ring 25, for example, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), polycarbonate (PC), fluorine based resin, ceramic, and the like. It should be noted that in the separation wall 21 only a portion contacting the slurry can be made of such a material.

On the surface of the polishing pad 12, hollows, for example, recesses or dimples, generally exists. The liquid cooling medium collected in the hollow can reach into the polishing area 43 to dilute the slurry. To prevent it, it is effective to add a brush 36 on the inner corner (Y side) of the separation wall 21.

Above the polishing pad 12 in the polished region 43, the slurry supply tube 31 for supplying a slurry and a pure water supply tube 33 for supplying pure water for water polishing to the polished region 43 are each provided. The slurry supply tube 31 and the pure water supply tube 33 are able to drop the slurry and the pure water respectively to a place in the upstream side of the rotation direction of the polishing pad 12 in relation to the top ring 25 and in a position close to the rotation center of the polishing pad 12. It should be noted that the place on which the slurry and the pure water are dropped can be changed by moving liquid dropping ports of the slurry supply tube 31 and the pure water supply tube 33. Components of the slurry are different by an object of CMP. The slurry is dispersion liquid of polishing grains to which a chemical is added in general, in case that the object is made of tungsten, alumina dispersion liquid to which iron nitrate is added.

Above the polishing pad 12 in the unpolished region 41, the cooling medium supply tube 35 with a showerhead for supplying a cooling medium is provided. The cooling medium supply tube 35, provided in a proper position of the polishing pad 12, a position close to the rotation center for example, is capable of dispersing a cooling medium of pure water. Here, supply of the cooling medium is performed with the showerhead with numerous pores instead of a tube with a single opening. This is for the purpose of increasing chances of contact between the cooling medium and the polishing pad 12 thereby to improve a cooling efficiency. It should be noted that when a semiconductor wafer 27 having a comparatively small diameter, a cooling medium supply tube 35 with a single opening can be used.

A place to which the cooling medium is supplied can be changed by moving the showerhead (supply port) of the cooling medium supply tube 35. Further, by changing an orientation of the showerhead (supply port) of the cooling medium supply tube 35, a direction in which the cooling medium is supplied can be changed. A flow amount, a temperature or the like of the cooling medium can be optimized. When the temperature of the cooling medium is to be made lower than a room temperature, a cold heat source (not shown) for example is wound around the cooling medium supply tube 35 thereby to cool the cooling medium. It should be noted that a moving system of the cooling medium supply tube 35 and the shower head, a flow amount control system, a temperature control system and the like are not shown. Further, the cooling medium can be water to which a surfactant is added, other than pure water. In such a case, an effect of washing the polishing pad 12 soiled by adhesion of the polishing grain can be expected secondarily. Further, the cooling medium is not limited to liquid, but gas such as nitrogen and atmosphere can be used.

Next, a polishing method using the polishing device 1 will be described.

In the polishing device 1, as described above, the polishing pad 12 is attached on the turntable 11. The U-shaped separation wall 21 sectioning the polishing pad 12 into the unpolished region 41 and the polished region 43 is fixed to the casing 15 by the press jig 23. The separation wall 21 is made to abut on the polishing pad 12. As a result, the unpolished region 41 is secured continuously from the center of the polishing pad 12 in an outer periphery direction.

The turntable 11 is rotated at a predetermined rotation speed, at 60 rpm for example. Then, above the rotated polishing pad 12, in the unpolished region 41 sectioned by the separation wall 21, the cooling medium is supplied via the cooling medium supply tube 35. The cooling medium spreads from the center of the polishing pad 12 in the unpolished region 41 in the entire outer periphery direction. Part of the cooling medium is made to flow to an outer periphery side by a centrifugal force due to rotation of the polishing pad and falls into the funnel 16. Other part of the cooling medium hits against the separation wall 21 (the part 21B) in the rotation direction downstream side of the polishing pad 12, moves along a wall surface of the curved separation wall 21 (the part 21B), and falls into the funnel 16. The flow amount of the cooling medium is about 200 cm³ per minute (200 ml/min) for example.

The slurry is dropped in the polished region 43 sectioned by the separation wall 21 on the rotated polishing pad 12, via the slurry supply tube 31.

Thereafter, the top ring 25 holding the semiconductor wafer 27 is conveyed to right above the polished region 43, and is let down while being rotated at a predetermined rotation speed, at 63 rpm for example. Further, the top ring 25 is pressed at a predetermined pressure, at 19.6 kPa (200 gf/cm²) for example, and the surface to be polished, the semiconductor device surface for example, of the semiconductor wafer 27 is made contact with the surface (polish contact surface 37) of the polishing pad 12. Polishing proceeds by rubbing the semiconductor device surface of the semiconductor wafer 27 against the polishing pad 12 on which the slurry is distributed.

Part of the slurry of the polished region 43 is made to flow to the outer periphery side by the centrifugal force by the rotation of the polishing pad 12 and falls into the funnel 16. Other part of the slurry hits against the separation wall (the part 21A) in the downstream of the polished region 43 (upstream of the unpolished region 41) and moves along the wall surface of the curved separation wall 21 (the part 21A), discharged into the funnel 16.

When polishing of a predetermined thickness is finished, supply of the slurry is stopped. Subsequently, pure water for water polishing is dropped from the pure water supply tube 33 and water polishing is performed, whereby the slurry adhered to the semiconductor wafer 27 is rinsed away. When water polishing is finished, supply of the cooling medium is stopped. However, supply of the cooling medium can be stopped or reduced when polishing is finished. It is because friction heat at the time of water polishing is small since a load at a time of water polishing is generally smaller than a load at a time of polishing.

The semiconductor wafer 27 on which water polishing after polishing is finished is conveyed to a post-polishing module (not shown) and a post-polishing process is performed. In the same time, usual dressing is performed by a dresser (not shown) on the polishing pad 12. This dressing is performed by rubbing the dresser against the polishing pad 12. If dressing is performed after the top ring 25 is retracted, there is no problem if an operation region of the top ring 25 and an operation region of the dresser overlap with each other. After dressing is finished, the top ring 25 holding a semiconductor wafer 27 to be polished next is conveyed to right above the polished region 43, and the semiconductor wafer 27 is similarly polished.

As stated above, the polishing method in the polishing device 1 in which the separation wall 21 is provided is not basically different from that of a polishing device without a separation wall 21. However, slurry gradually adheres to the separation wall 21 in the polished region 43. Thus, if such an adherent drops and reaches beneath the semiconductor wafer 27 under being polished, a scratch may be sometimes generated in a surface to be polished of the semiconductor wafer 27. Therefore, it is preferable to add a removing process of such an adherent. For example, every time a predetermined number of semiconductor wafers 27 is processed, a procedure is performed in which the separation wall 21 is made in a state of being held up from the polishing pad 12 and washed with a hand shower or the like. Further, it is possible to make a system capable of performing such washing automatically.

Next, an effect obtained by CMP by using the polishing device 1 will be described.

Note a temperature distribution in a measure line 45 (two dot chain line) in a neighborhood of the top ring 25 on the polishing pad 12, shown in FIG. 1B. The measure line 45 is a line located in a radial direction of the polishing pad 12 and included in the polish contact surface 37. Besides, the measure line 45 is positioned in a downstream side of the top ring 25 in relation to the rotation direction of the polishing pad 12. A temperature in the measure line 45 is measured by a radiation thermometer. Since this temperature is a temperature of the polishing pad 12 soon after polishing, this temperature can be substituted for a temperature of the polishing pad 12 directly under the semiconductor wafer 27.

FIG. 2 is a graph indicating a position of the measure line 45 by a horizontal axis and a temperature by a vertical axis. In a polishing device without cooling, that is, in a conventional polishing device, the temperatures exceed 50° C. and are approximately 60° C. in a center portion. On the other hand, in a polishing device with cooling, that is, in the polishing device 1 of the present embodiment, the temperatures including a temperature in the center portion are equal to or lower than 40° C. Further, in the polishing device 1, a difference between a maximum temperature and a minimum temperature is decreased.

Therefore, in the polishing device without cooling, that is, in the conventional polishing device, the polishing pad 12 is softened due to temperature rise. Therefore, a planarization characteristic of polishing is deteriorated and a global level difference (difference in height between the highest place and the lowest place) due to polishing of the semiconductor wafer 27 reaches as much as 100 nm. On the other hand, in the polishing device with cooling, that is, in the polishing device 1 of the present embodiment, softening of the polishing pad 12 is suppressed since temperature rise is suppressed. Therefore, a planarization characteristic of polishing is maintained and a global level difference (difference in height between the highest place and the lowest place) due to polishing of the semiconductor wafer 27 is suppressed to 20 nm.

Second Embodiment

A polishing device and a polishing method according to a second embodiment will be described with reference to FIG. 3. What is different from the polishing device 1 of the first embodiment is that a separation wall has a dogleg shape in plain view. It should be noted that the same reference numeral is given to the same component as that in the first embodiment and explanation thereof will be omitted.

As shown in FIG. 3, in a polishing device 2, a separation wall 51 has a dogleg shape, while the separation wall 21 in the polishing device 1 of the first embodiment has the U shape. In the dogleg-shaped separation wall 51, two places contacting an outer periphery of the polishing pad 12 are apart from each other by about one fourth of the outer periphery along the outer periphery of the polishing pad 12. Here, a distance between press jigs 23 is larger compared with that in the first embodiment.

Consider to divide the dogleg-shaped separation wall 51 in plain view into two portions 51A, 51B (first and second curved portions) at a bent portion. The portions 51A, 51B each correspond to each of portions (portions 21A, 21B) of the U-shaped separation wall 21 of the polishing device 1 of the first embodiment, the separation wall 21 cut in a manner that the two portions become plane symmetry. In other words, in a rotation direction upstream of the polishing pad 12 in a polished region 41, the portion 51A has a curb projecting toward the upstream. The portion 51B also has, in a rotation direction downstream of the polishing pad 12, a curb projecting toward the upstream. The bent portion (border between the portions 51A, 51B) in the dogleg shape in plain view of the separation wall 51 is positioned in a center portion of the polishing pad 12. Other constitutions are the same as those of the polishing device 1 of the first embodiment. The polishing method is also the same as that in the polishing device 1 of the first embodiment.

With regard to the separation wall 51, in the unpolished region 41, a curvature in the downstream side is reverse to a curvature in the first embodiment. As a result, in the polishing device 2 it is easy to dispose the top ring 25 close to the separation wall 51. Since the cooled polishing pad 12 reaches directly under the top ring 25 in a short time, a cooling efficiency is improved. It should be noted that the shape of the separation wall 51 can be changed from the dogleg shape to a V shape. In other words, the portions 51A, 51B are each to have a linear shape instead of a curved shape. In such a case, a position of the top ring 25 is required to be apart from the dogleg-shaped separation wall in some degree, but a V-shaped separation wall 51 is easy to be formed.

The polishing device 2 similarly has the effect the polishing device 1 of the first embodiment has.

Third Embodiment

A polishing device and a polishing method according to a third embodiment will be described with reference to FIG. 4A and FIG. 4B. What is different from the polishing device 1 of the first embodiment is that a plurality of cooling medium supply tubes is provided. It should be noted that the same reference numeral is given to the same component as that in the first embodiment and explanation thereof will be omitted.

As shown in FIG. 4A and FIG. 4B, a polishing device 3 is provided with a plurality of cooling medium supply tubes 55. Other constitutions are the same as those in the polishing device 1 of the first embodiment. The cooling medium supply tubes 55 are disposed in a manner that their supply ports cover a donut-shaped polish contact surface 37 in a radial direction almost linearly from a center of a polishing pad 12 in an outer periphery direction along a radius in an unpolished region 41.

Each of the cooling medium supply tubes 55 can be independently controlled in terms of a temperature of a cooling medium, a flow amount, and a position of the supply port. It should be noted that it is possible that one cooling medium supply tube 55 is constituted to have a plurality of supply ports and that three cooling medium supply tubes 55 are provided for example thereby to supply the cooling medium from six supply ports.

Further, the supply port of the cooling medium supply tube 55 can be a showerhead. Further, with regard to the cooling medium supply tubes 55, an array of the supply ports are not limited to a linear array in a radial direction. The supply ports can be disposed curvedly along a separation wall 21 for example so that a temperature distribution of a polishing pad 12 can be better controlled. Further, the separation wall 21 can be replaced by the separation wall 51 of the second embodiment.

The polishing method by the polishing device 3 is the same as that of the polishing device 1 of the first embodiment except that the cooling medium is supplied from plural cooling medium supply tubes 55.

In the polishing device 3 it is possible to make the temperature distribution of the polishing pad 12 have a desired shape by independently controlling temperatures, flow amounts and the like of the plural cooling medium supply tubes 55. In other words, it is possible to make the temperature distribution on the measure line 45 shown in the first embodiment be flat as shown in FIG. 5. This is attained by lowering the temperature of the cooling medium at the center portion of the polish contact surface 37 among the plural cooling medium supply tubes 55 or increasing the flow amount of the cooling medium at the center portion.

By performing a CMP processing by using the polishing device 3 in which such a temperature distribution of the polishing pad 12 is realized, it is possible, in a semiconductor wafer 27, to make a characteristic of a semiconductor device formed therein more uniform.

The polishing device 3, in addition, similarly has the effect the polishing device 1 of the first embodiment has.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not instead to limit the scope of the inventions. Indeed, the novel methods and devices described herein may be embodied in a variety of other forms; furthermore, various emissions, substitutions and changes in the form of the methods and devices described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms of modifications as would fall within the scope and spirit of the inventions.

For example, in the embodiment there is described an example of the separation wall in which two places contacting the outer periphery of the polishing pad are apart from each other by about one fourth of the outer periphery of the polishing pad. In contrast, it is also possible to set two places to be apart from each other by less than or more than one fourth of the polishing pad outer periphery. It suffices if desired cooling of a polishing pad is performed in an unpolished region sectioned by a separation wall. 

1. A polishing device, comprising: a rotatable turntable on an upper surface of which a polishing pad is attached; a holding unit rotatably holding an object to be polished and disposing a polished surface of the object to be polished in a manner to face the polishing pad; a separation wall abutting on the upper surface of the polishing pad and sectioning the polishing pad into a polished region in which said holding unit is provided and an unpolished region in which said holding unit is not provided; a slurry supply tube supplying a slurry to the upper surface of the polishing pad in a polished region; and a cooling medium supply tube supplying a cooling medium to the upper surface of the polishing pad in the unpolished region.
 2. The polishing device as set forth in claim 1, wherein the polished region and the unpolished region includes a donut-shaped polish contact surface made as a result that the polishing pad being rotated contacts the holding unit.
 3. The polishing device as set forth in claim 1, wherein said separation wall has a U shape in plain view and a bottom portion of the U shape is disposed in a neighborhood of a rotation center of the polishing pad.
 4. The polishing device as set forth in claim 1, wherein a constitution material of at least a part of a surface of said separation wall contains any one of polyether ether ketone (PEEK), polyphenylene sulfide (PPS), and fluorine.
 5. The polishing device as set forth in claim 1, wherein said cooling medium supply tube is movable in a radial direction of the polishing pad.
 6. The polishing device as set forth in claim 1, wherein said cooling medium supply tube supplies a temperature-controlled cooling medium.
 7. The polishing device as set forth in claim 1, wherein a plurality of said cooling medium supply tubes is provided along a radial direction of the polishing pad and said cooling medium supply tubes are each independently controlled to supply the cooling medium.
 8. The polishing device as set forth in claim 1, wherein said cooling medium supply tube has a showerhead with numerous pores facing the upper surface of the polishing pad.
 9. The polishing device as set forth in claim 1, wherein the cooling medium is pure water.
 10. The polishing device as set forth in claim 1, wherein the cooling medium is gas.
 11. A polishing method, comprising: preparing a rotatable turntable on an upper surface of which a polishing pad is attached; preparing a holding unit rotatably holding an object to be polished and disposing a polished surface of the object to be polished in a manner to face the polishing pad; making a separation wall abut on the polishing pad and sectioning the polishing pad into a polished region in which the holding unit is provided and an unpolished region in which the holding unit is not provided; rotating the turntable thereby to rotate the polishing pad; supplying a cooling medium cooling a surface of the polishing pad in the unpolished region; supplying a slurry in the polished region; and rotating the object to be polished and pressing the object to be polished to the polished region to which the slurry has been supplied.
 12. The polishing method as set forth in claim 11, wherein the separation wall has a U shape in plain view and a bottom portion of the U shape is disposed in a neighborhood of a rotation center of the polishing pad.
 13. The polishing method as set forth in claim 11, wherein a constitution material of at least a part of a surface of the separation wall contains any one of polyether ether ketone (PEEK), polyphenylene sulfide (PPS), and fluorine.
 14. The polishing method as set forth in claim 11, wherein the cooling medium supply tube is movable in a radial direction of the polishing pad.
 15. The polishing method as set forth in claim 11, wherein the cooling medium supply tube supplies a temperature-controlled cooling medium. 